The invention relates to platelet-shaped pigments based on iron oxide which contain aluminum oxide in solid solution.
There is a continuously increasing demand for effect pigments with which metallic-like effects can be achieved, for example, in lacquers, plastics, glass, ceramics or cosmetics. In addition to naturally occurring and synthetic platelet-shaped iron oxides, which can be prepared in different colors and shapes by hydrothermal processes, platelet-shaped iron oxide pigments which contain aluminum oxide incorporated as a solid solution, that is to say in the haematite crystal lattice, are also known from European Patent Specification No. 68,311 and U.S. Pat. No. 4,373,963. These pigments are distinguished by a very good gloss and can be prepared in different sizes and thicknesses and different red shades by varying the process conditions of the hydrothermal process.
It is also known from U.S. Pat. No. 4,373,963 that such pigments can be provided with an external coating of titanium dioxide and in addition to the body color, an interference color which varies according to the layer thickness of the opaque TiO.sub.2 layer can thereby be generated.
Although these known pigments are particularly suitable for many applications, there is still a need for pigments with which on the one hand the color range accessible and on the other hand the possible uses of the pigments can be increased.